Biogas from dairy farm ponds Stephan Heubeck & Rupert Craggs - - PowerPoint PPT Presentation

Biogas from dairy farm ponds

Stephan Heubeck & Rupert Craggs

Hamiltion

• 22. April 2015

National Institute of Water & Atmospheric Research Ltd, New Zealand

Why bother with pond biogas systems? Because we can address more than one problem at once!

Why bother with pond biogas systems?

“Look deep into nature, and then you will understand everything better” Albert Einstein

NIWA pond monitoring programs

Obtaining methane production data in the field

Storage pond sites 2013

• Monitoring sites in Northland, Waikato and

Southland

• Farms of high and low intensity
• (use of feed pads, stocking rate)
• Pond biogas production + quality
• Raw effluent quantity
• Raw effluent quality:
• Solids - TS/VS, COD
• Nitrogen - TN
• Phosphorus - TP

2013 storage pond monitoring

Pond temperature shows seasonal variation:

• Minimum pond bottom: ~ 7oC
• Minimum pond water: ~ 3oC

2013 storage pond CH4

Southland storage pond:

• Correlates with number of cows milked
• Autumn reduction due to single milking

2013 storage pond CH4

Waikato storage pond:

• Milk throughout winter – more constant load
• Greater correlation of CH4 production with

solids load than temperature

Per cow solids loading:

• Southland:

0.29 kgTS/0.18kgVS /cow/day

• Waikato:

1.13 kgTS/0.82kgVS /cow/day  feed pad

Methane productivity:

• Southland:

0.21 m3CH4/kgVS

• Waikato:

0.22 m3CH4/kgVS

2013 storage pond summary

2013 storage pond methane emissions:

• Southland:

6.7 kgCH4/cow/year

• Northland:

8.3 kgCH4/cow/year

• Waikato:

34.1 kgCH4/cow/year feed pad – more solids 2012 anaerobic pond methane emissions:

• Southland:

14.37 kgCH4/cow/year

• Northland:

14.45 kgCH4/cow/year

• Waikato:

7.68 kgCH4/cow/year

Methane GHG Emissions

Pond monitoring summary

Dairy farm effluent ponds minus side:

• Release much more GHG emissions (methane)

than previously assumed

• Emissions will increase with farm intensification

Dairy farm effluent ponds plus side :

• Conversion of VS to CH4 similar to engineered

digesters

• Very good at removing (coarse) solids
• Simple to build
• Simple to operate
• Can cover to capture odour and GHG
• Biogas energy potential

Basics:

• For flush manures and dilute wastes only
• Solids concentrations up to ~5%
• Different retention times for solids and liquids
• Loading rates <0.5 kgVS/m3/day
• Retrofits possible

NIWA Covered Anaerobic Pond Design

Custom designed covered anaerobic pond:

• Deep, narrow and long pond
• Dedicated pond often better than retrofit
• Covering (shallow) storage pond often

uneconomic

• Liner depending on regulation (plastic, clay)

NIWA Covered Anaerobic Pond Design

NIWA Covered Anaerobic Pond Design

Simple cover:

• Common cover materials (LLDPE)
• Flexible, UV resistant, cost effective
• Weight pipes for rainwater guidance
• Electric rainwater draw off pump
• Ring pipeline for efficient biogas draw-off
• No floatation underneath cover

Biogas is the most versatile renewable energy resource - usage options include:

• Flaring – GHG and odour control
• Combined heat and power (CHP) – generator
• Heat – boiler use
• Transport fuel – purification and compression

There is no size that fits all!

Biogas use options

Biogas flaring

Biogas flaring:

• Low maintenance
• Odour and GHG

control

• No local heat

demand

• Small electricity

demand

• Not big enough for

advanced biogas use options like vehicle fuel etc.

Biogas CHP

Motor-generators:

• Spark ignition
• Gas purification for

generator longevity

• Grid synchronisation
• r stand alone
• Radiator heat

recovery

• Exhaust heat

recovery

• Renewable 3-phase

electricity on call

• With biogas storage

back-up function for grid outages

Biogas CHP

Waste heat use:

• 80-90 C hot water
• 2 kWh hot water for every

1 kWh electricity

• Hot water for washing and

heating

• Hot water can be stored

independently to decouple electric and thermal load

Biogas as boiler fuel

The “overlooked” option:

• Far simpler to operate than CHP
• Little (no) biogas purification required
• Highly efficient biogas use: 90 – 102% efficiency
• Doable at small scale
• Financial attractiveness can be good as well

Biogas transport fuel

Biogas as transport fuel:

• Purified and compressed biogas (bio-methane)

can be used in any CNG vehicle

• The size of the biogas resource on NZ farms may

be often too small to justify the high investment

• Further increases in the cost of petroleum fuels

may however make this option attractive in the future

So how much does a covered anaerobic pond based biogas system cost, and does it make financial sense?

Biogas from covered anaerobic ponds

The answer depends, because:

• Every farm is different

(size, soil, existing gear)

• A lot of covered

anaerobic ponds will be built without biogas use

As solids removal technology:

• Dry matter (DM) reduction higher than with

mechanical solids separator or weeping wall

• Cost less than mechanical solids separator and

about equal to weeping wall

• No odour or GHG emissions
• Maintenance more flexible

Covered Anaerobic Ponds

Covered Anaerobic Pond pre-treatment prior to storage pond:

Covered Anaerobic Ponds

Covered Anaerobic Pond treated effluent ready for:

• Recycling as wash water, i.e. through backing

gate

• Injection into low application sprinkler system (K-

line) or centre pivot irrigator

Covered Anaerobic Ponds

Covered Anaerobic Ponds

As compliance tool:

• Reduce effluent odour  see pig industry
• Reduce GHG emissions  the dairy industry’s

chance to reduce the GHG foot-print by 10 – 20% with here and now technology without curtailing production

Indicative costs

Assuming a 600 cow dairy farm with feed pad. Covered Anaerobic Pond added to existing storage pond system for pre-treatment:

Earth works: $15k – $25k$ (cut and fill or import?) Plastic: $15k - $35k (bottom liner required?) Pond pipe work: $5k - $10k Consents, Planning, Supervision: ???? Biogas piping and conditioning: $5k - $15k Biogas boiler: $3k - $6k Biogas CHP: $30k - $80k (longevity, only ~2,500 h/y!) Installation and connections: $5 - $30k (lines company decides)

Biogas value

Assuming a 600 cow dairy farm with feed pad: Annual electricity consumption: 80k – 120k kWh/y Thereof hot water (heat): 25k – 30k kWh/y Annual usable electricity generation: 50k – 70k kWh/y Annual usable hot water generation: 25k – 30k kWh/y Gross earnings biogas boiler: $3k/y - $7k/y (D/N tariff!) Gross earnings biogas CHP: $15k/y - $30k/y (lines charging structure and / or islanding of generation will have a big impact on net result)

Biogas use

The early (mass) adopters for covered anaerobic pond based biogas technology will therefore be piggy-backed schemes where the pond is in place for other reasons:

• Biogas system payback = payback of gas user
• Can be economic for small (gas boiler) and

large schemes (CHP)

• Economic threshold of <3 years doable

Covered anaerobic pond based biogas systems will likely be installed for their multiple benefits: Solids removal; effluent reuse;

• dour/GHG emission reduction

Biogas energy will be the icing on the cake

Conclusion